1. Field of the Invention
This invention generally relates to image processing technology for combining two or more picture patterns into a single picture frame for display on a picture tube such as a T.V. set, and particularly to an image processing system for displaying a picture frame by combining a motion picture pattern, which may be varied under the control of the operator, with a still picture pattern which defines the background of picture frame. More specifically, the present invention relates to a T.V. game system in which motion picture information and still picture information are controlled independently from each other and they are combined into a series of frames which are then displayed on the T.V. screen.
2. Description of the Prior Art
FIG. 1a shows a prior art T.V. game system which includes a picture processing unit (hereinafter, also referred to as "PPU") 1 which comprises a random access memory (hereinafter, also referred to as "RAM") and is connected to a video memory 2 and to a central processing unit (hereinafter, also referred to as "CPU") 3, which, in turn, is connected to a main memory 4. In the system of FIG. 1a, under the control of CPU 3, motion and still picture data are transferred from the main memory 4 to the video memory 2 to be stored therein temporarily, and then the PPU 1 receives appropriate data from the video memory 2 and to supply an output as a video signal to a T.V. set (no shown) for display under the control of the CPU 3. A memory map contained in the video memory 2 is shown in FIG. 1b, and, as shown, the memory map includes a motion picture character pattern generating area 2-1, a motion picture attribute table 2--2 which is rewritten for each frame to be displayed during the vertical blanking period, a still picture character pattern generating area 2-3, a still picture character pattern name table 2-4 and a still picture color table 2-5.
Describing the operation of the above-described system with reference to FIG. 2, during the horizontal blanking period in carrying out scanning along horizontal line sectors, the motion picture attribute table 2--2 is accessed under the control of the operator thereby retrieving the attributes of motion picture pattern to be displayed in the next scanning line. Then, on the basis of the thus retrieved attributes, desired motion picture character pattern data is outputted from the motion character pattern generating area 2-1 during the same horizontal blanking period thereby generating a motion picture pattern. On the other hand, as the line scanning of the display screen proceeds, a pattern name and a color code are read out from the addresses, which corresponds to a display position, of still picture character pattern name table 2-4 and the still picture color table 2-5, respectively. On the basis of the pattern name thus read out, a pattern data is outputted from the still picture character pattern generating area 2-3 so that a still picture pattern is generated in real time. If there occurs a collision between the still picture pattern data and the motion picture pattern data at the same position on the display screen, either one of them is allowed to be displayed in accordance with a predetermined priority.
In the above-described prior art system, since external address and data buses are used to call and obtain still picture character data during the line scanning period and also the number of pins usable for interconnections between components is limited, the retrieving of the motion picture attribute table and the calling of motion picture character pattern data on the basis of the result of such retrieval must all be carried out during the horizontal blanking period. For this reason, the number of motion picture characters which may be displayed during a single line scanning period is rather limited as is the kind of motion picture characters which may be displayed in a single frame. As a result, displayed pictures tend to be dull and they do not change as fast as pleasing to a viewer.